This invention concerns air filters and more particularly disposable air filters of a type in common use with heating, air conditioning and ventilation (HVAC) systems.
Such filters are designed to be disposable since they become dirty and clogged in a relatively short time and are not easily cleanable.
The usual arrangement invoices generally planar fibrous air filter element fixed in a paperboard frame which supports the air filter element.
The filter element and frame being integrally connected together are discarded as a unit.
A significant disadvantage of such disposable air filters, is that their relative bulkiness increases the shipping costs and may occupy significant storage space if large numbers of filters are involved.
For this reason, it would be advantageous if the filters could be made to be more compact for shipping and storage.
One approach is to make the filter elements separable from the frame and to be configured to be able to be folded up for storage and then expanded when installed in the frame.
The filter elements themselves could then be kept in a compact state when being stored or shipped. However, it is important that the filter be easily installed in the frame and would not allow excessive bypass of unfiltered air flow around the separate filter element.
Disposable air filter elements usually need to be installed with a planar restraint such as a metal screen or lattice also held in the frame so as to prevent the filter element from being dislodged as a result of forces exerted on the element by the air flowing through the filter element.
Air filter elements are also typically made of porous paper or fiber and are somewhat vulnerable to being torn or otherwise damaged by incidental contact with the planar restraint, allowing unfiltered air to pass through the tears in the filter element.
Another desirable feature of such filters is that the air filter element should be easily and quickly installed so as to be sealed to the frame to minimize the volume of unfiltered air flowing around the filter element.
It is an object of the present invention to provide an air filter of a type in which a filter element is separable from a permanent holder frame and is easily folded up into a compact state when not in service, such as when being shipped or stored, but easily expanded after being installed in a frame to be placed in service.
It is a further object of the present invention to provide such a separable filter element which is protected from being torn by being contacted with an associated filter element restraint.
It is yet another object to provide a sealing engagement between the expanded filter element and the frame which minimizes the volume of air flow around the air filter element.